1. Field of the Invention
The invention relates to display devices, and in particular to display devices with low power consumption and high aperture ratio.
2. Description of the Related Art
Liquid crystal displays (LCDs) are used in a variety of applications including calculators, watches, color televisions, computer monitors, and many other electronic devices. Active matrix LCDs are a well known type of LCD. In a conventional active matrix LCD, each picture element (or pixel) is addressed using a matrix of thin film transistors (TFT) and one or more capacitors. The pixels are arranged and wired in an array having a plurality of rows and columns. For example, a SVGA display is a matrix of 2400×600 pixels.
To address a particular pixel, the proper row is switched “on” (i.e., charged with a voltage), and a voltage is sent down the correct column. Since other intersecting rows are turned off, only the TFT and capacitor at the particular pixel receives a charge. In response to the applied voltage, the liquid crystal within the cell of the pixel changes its rotation and tilt angle, and thus, the amount of light is absorbed or passing therethrough. This process is then repeated row by row.
In liquid crystal cells of a pixel, the magnitude of applied voltage determines the amount of light is absorbed or passing therethrough. Due to the nature of liquid crystal material, the polarity of the voltage applied across the liquid crystal cell must alternate. Therefore, for an LCD displaying video, the voltage polarity applied to the liquid crystal cells is inverted (or reversed) on alternate frames of the video. This process is known as inversion.
Unfortunately, if the polarity of the entire LCD is inverted with the same polarity on alternate frames, the LCD flickers at an unacceptable level. Hence, many conventional LCDs use other forms of inversion, such as line inversion or dot inversion. In line inversion, alternate columns or rows of an LCD are inverted on alternate frames (e.g., in a “striped” pattern). Dot inversion inverts alternate pixels of each row and column alternate frames (e.g., in a “checkerboard” pattern). Of the two inversion techniques, dot inversion is generally considered to produce higher display quality.
However, inversion, especially dot inversion, increases power consumption of the LCD, since the data lines behave as a capacitive load (and may also include a storage capacitor), and thus, consume power as their voltages change polarity. Since LCDs are often used in battery powered or low power devices, many LCDs use driving methods optimized for power consumption. For example, many LCDs use line inversion rather than dot inversion.
Accordingly, it is desirable to develop display devices and driving methods with low power consumption.